Automotive radiators and other heat exchangers have a series of parallel flat tubes carrying a hot fluid, such as engine coolant, for transfer of heat to a cooler medium, such as air, which flows around the tubes. To improve heat transfer rate, sinuous or corrugated metal strips called fins or air centers are inserted in the spaces between the flat tubes and soldered or brazed at the junction of the peaks of the air centers and the tubes to assure good heat conductivity from the tubes to the fins. The tubes are assembled in the radiator at fixed spacings and the air centers then must be manufactured to fit in the spacing. Different products may have different heat transfer requirements and thus require centers with different fin spacings or lengths. It is desirable to reliably provide an accurate part length having a preset number of convolutions per part.
It is known to make corrugated fins from sheet stock in a machine with forming rolls for producing a set number of corrugations peaks or convolutions per unit length of strip stock, stuffing rolls to stuff or pack the fins such that the convolutions are touching, then feeding the fins by metering rolls and stretching out the fins by pullout rolls until the desired pitch is obtained. The number of teeth in the pullout rolls and the tooth form determines the nominal fin spacing or density. The corrugated material is stretched between the metering rolls and the pullout rolls during machine set up to achieve substantially the correct fin pitch or density, and to operate the rolls in phase so that the pitch remains the same. The fin is cut into pieces having equal numbers of corrugations so that the part length is then determined by the pitch. It is also known to drive the pullout rolls by a servomotor and to make adjustment of the phase of the pullout rolls through servomotor control to change fin pitch during operation for correction of part length. This is accomplished by detecting whether a cut part is too long or too short and adjusting the phase by a preset increment to make a gross change in the size of the next part without consideration of the amount of deviation of the part length from a target value.